1,721,025 research outputs found
Synthesis and characterisation of calcium sulfoaluminate cements produced by different chemical gypsums
No full textCalcium sulfoaluminate (CSA) cements show some desirable environmentally friendly features which include the possibility of using several industrial by-products as raw materials in their manufacturing process. Four chemical gypsums (flue-gas desulfurisation gypsum, fluorogypsum, phosphogypsum and titanogypsum) have proved to be suitable as total substitutes for natural gypsum (NG) in the raw meal. Mixtures based on limestone, bauxite, NG or one of the CS-rich ̄ by-products were heated in a laboratory electric oven from 1150 to 1300°C. The reactivity of raw mixtures to form clinker products was evaluated using X-ray diffraction (XRD) analysis. The raw mixtures containing industrial gypsum displayed better reactivity towards C 4 A 3 S ̄ than the one made with NG. Moreover, conduction calorimetric measurements associated with XRD and differential thermal-thermogravimetric analyses showed that all CSA cements, obtained by adding commercial anhydrite to clinkers produced at the optimum synthesis temperatures, have similar hydration products but with different hydration kinetics
Influence of microsilica on the hydration of ye’elimite
No full textOne of the promising opportunities for a more environmentally friendly cement manufacture is the production of a clinker based on calcium sulfoaluminate (CSA). Although CSA clinkers may have quite variable compositions, their main component is ye’elimite. Like ordinary Portland cements, CSA cements, which are obtained by intergrinding CSA clinkers with calcium sulfate, may be blended with supplementary cementitious materials such as slag, fly ash or microsilica in order to modify their properties and to further improve their CO2 balance.
In this paper the influence of microsilica on both the hydration kinetics and hydrate assemblage of synthetic ye’elimite is presented. Blends of ye’elimite and microsilica with and without addition of gypsum were examined. The hydration experiments were carried out using water or 0.1 molar KOH solution at a water/solid ratio of 2. KOH solution was chosen in order to stimulate the dissolution of microsilica.
Conduction calorimetry, thermogravimetric and X-ray diffraction analyses were employed in order to follow hydration kinetics and to assess the hydration products. Thermodynamic modeling using the geochemical speciation code GEMS-PSI was carried out to calculate the stable hydrate assemblages and to compare those results with the experimental data.
It was found that microsilica accelerates early hydration kinetics of ye’elimite probably due to the filler effect. This is especially the case for the systems without gypsum which exhibit much slower hydration kinetics than the systems with gypsum. Besides the effect on hydration kinetics, microsilica influences the hydration reaction of ye’elimite. Plain ye’elimite hydrates to monosulfate and aluminum hydroxide. When increasing amounts of microsilica are added, higher amounts of ettringite can additionally be observed. Besides, strätlingite occurs as further crystalline hydration product. As a result ye’elimite is able to hydrate in the presence of silica to form ettringite, strätlingite and aluminum hydroxide. This reaction path agrees well with stable phase assemblages calculated by thermodynamic modeling.
KOH solution was found to accelerate early kinetics compared to the samples hydrated with water; furthermore, it promotes the dissolution of microsilica, inasmuch a higher amount of strätlingite is present after 28 days of hydration compared to reaction in pure water
Further studies of the hydration of MgO-hydromagnesite blends
No full textThe hydration of magnesium oxide in the presence of hydromagnesite (Mg5(CO3)4(OH)2·4H2O) was investigated. The hydration products are a poorly-crystalline form of brucite (Mg(OH)2) and an unknown amorphous or poorly crystalline hydrate, which was evidenced by X-ray diffraction analyses and Raman spectroscopy. By thermogravimetry it was found that in the presence of hydromagnesite more water is bound in hydrate phases than can be explained by the formation of brucite only. The unknown hydrate is hypothesized to lead to cohesive binding in MgO-hydromagnesite blends. Due to thermodynamic predictions artinite (Mg2(CO3)(OH)2·3H2O) should be the stable hydrate in this system. The addition of artinite crystal seeds, however, had no significant effect on hydration kinetics or nature of the reaction products. The hypothesis that the addition of sodium bicarbonate (NaHCO3) could modify or accelerate the hydration reactions due to its high solubility and the supply of additional HCO3− ions was also not supported by the experiments
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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